Yet while they were winless, the hard-core conservatives intent on selecting a Senate more to their liking this year were far from utterly defeated. All of the challenged GOP incumbents reacted to the pressure by working to reconfirm their credentials with conservatives. This held true even for those whose credentials should have been least in doubt.

Having induced this embrace of their policies and principles, the GOP's most conservative wing can surely claim a kind of success. And that claim can be shared by the populists who provided the votes as well as by the more organized entities that furnished the funding.

Meaningful as this rightward shift has been for the party and the Senate, the insurgent elements would have preferred to actually knock off a few of their targets. That would have meant more reinforcements for Rand Paul of Kentucky, Marco Rubio of Florida, Mike Lee of Utah and Ted Cruz of Texas — the four freshmen who shouldered aside the candidates of the GOP establishment on their way to the Senate in 2010 and 2012.

At the start of the 2014 primary season, a group called the Senate Conservatives Fund, which was co-founded by former Sen. Jim DeMint before he quit the Senate to become head of the Heritage Foundation, set out to bolster and bankroll long shots against Republicans it considered insufficiently loyal to the cause. Also active on the fundraising front were groups such as Tea Party Express, FreedomWorks and The Madison Project.

At first, the movement seemed to have a decent stable of horses ready to run in states like Texas and Oklahoma, Kansas and Kentucky, Georgia and Arizona. But several of the early recruits proved distinctly disappointing. Others failed to generate competitive levels of donations. And in a few states, such as South Carolina, Tea Party votes were scattered among several challengers.

The anti-incumbent thrust was parried early in Kentucky, where Matt Bevin's once-promising bid against Senate Republican Leader Mitch McConnell fizzled in May. In the end, the closest the intraparty upstarts came was in Mississippi, where six-term veteran Thad Cochran needed two rounds of voting to fend off former state legislator Chris McDaniel (who is still contesting the outcome).

There is also some consolation in Ben Sasse of Nebraska, who won the GOP nod for a vacant seat. Sasse was backed by Cruz and Sarah Palin even though many Tea Party people in Nebraska preferred another candidate.

So why was this cycle so different from 2008 and 2010, when the Tea Party fever ran high and its favorites won primary after primary — even unseating such stalwart Republicans as Robert Bennett in Utah and Richard Lugar in Indiana?

Let's tick off five big reasons:

Lack of obvious targets. The list of Republican senators seeking re-election was fairly short and included no moderates other than Susan Collins in Maine. Conservatives in that state did not manage to find a suitable primary opponent for her, and she is heavily favored to win in the fall.

Lack of killer issues. In 2010 many Republicans were hard-pressed to explain their votes for TARP, the "bank bailout" of 2008-09 that populists saw as unconscionable welfare for Wall Street. In 2012, incumbents were dinged for not "stopping Obamacare." This year's assault on incumbents began with a far less potent charge: that they failed to back House Republicans in the 2013 government shutdown.

The novelty of the Tea Party in 2010 and the momentum that it carried through 2012 have weakened. So has the enthusiasm for political neophytes and outsiders. At the same time, many rank-and-file Republicans have come to see that inexperienced candidates from the right were losing in states where more conventional Republicans — such as Mike Castle in Delaware — would have won.

Republican incumbents have gotten the message. This is by far the most important. Most senators dealt early with vulnerabilities such as residency in their home state (a land mine for Lugar in 2012) or intraparty feuds back home. They took their opponents seriously, no matter how exotic they might seem. They made sure they had the establishment endorsements as always but added the backing of high-profile conservatives, talk show hosts and other popular figures in some cases. All in all, this class of GOP incumbents ran like they did when they were first elected, while using all the advantages and leverage of incumbency. No one got caught napping in 2014.

The cash advantage. Despite the new sources of money for the insurgents, it was the incumbents who raised record amounts of cash and spent it early. This allowed them to define and even attack their challengers rather than ignore them or hope they would disappear.